Author Topic: V8 cylinder firing order  (Read 1056 times)

Offline Vixen

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V8 cylinder firing order
« on: January 23, 2023, 04:36:32 PM »
This thread is to answer Ron Reid's firing order question, without hijacking Steamers Porsche 917 thread.

The Mercedes Benz W165 grand Prix engine (1939), which I am modeling, was unique. It was their only racing engine from the 'Silver Arrows' era, which had a V8 configuration; all the others were V12 or V16. Even today, Mercedes Benz remain very secretive about the technical details of those old engines.

There appear to be several viable firing orders for the cross plane crankshaft V8 engine. I would guess the same would apply to a V12 engine. Different engine manufactures make use different V8 firing orders and some even use different cylinder numbering conventions, just to add to the confusion. Here are a selection of firing orders and cylinder numbering conventions for some typical American V8 engines. You can see what I mean about potential confusions.




I knew the published firing order for the W165 was: 1-3-7-2-6-5-4-8, but I did not how the cylinders were numbered. I discovered that some Ford engines matched that firing order and I was then able to determine the cylinder numbering they had used. Coincidentally, it was the same cylinder numbering convention as Daimler Benz (Mercedes Benz parent company) used for all their V12 aircraft engines: DB601, DB605 etc. So, I felt confident I was on the right track

Once I had the firing order and the cylinder numbering convention, I could start drawing up the four overhead camshafts for my W165 engine.

Mike

« Last Edit: January 24, 2023, 01:31:47 PM by Vixen »
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Offline Roger B

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Re: V8 cylinder firing order
« Reply #1 on: January 23, 2023, 04:46:45 PM »
That's a bit of detective work  :)
Best regards

Roger

Offline steamer

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Re: V8 cylinder firing order
« Reply #2 on: January 23, 2023, 04:50:14 PM »
I find it interesting that it's was a cross plane crank!   I figuired  it would be a flat plane crank
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Offline Vixen

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Re: V8 cylinder firing order
« Reply #3 on: January 23, 2023, 05:00:48 PM »
Hello Dave,

I also would have expected them to have used a flat plane crank for a racing engine, effectively two four-in-line engines side by side on the same crank. I can only guess that the V8 was such a new departure from what they had done before that they chose the cross plane crank as low risk, as they were in everyday use on your side of the pond and elsewhere.

Who Knows?

Mike
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Offline Vixen

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Re: V8 cylinder firing order
« Reply #4 on: January 23, 2023, 05:05:52 PM »
That's a bit of detective work  :)

Roger,

You may find that some of the firing orders with alternative cylinder numbering may turn out to be the same. I did not have the patience or inclination to dig any further.

Mike
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Offline RReid

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Re: V8 cylinder firing order
« Reply #5 on: January 23, 2023, 08:45:32 PM »
Hi Mike. Thank you so very much for taking the time to respond so quickly and well to my question.

The 1-3-7-2-6-5-4-8 firing order strikes me as rather less intuitive than the others. Do you know what the reasoning behind that choice is?
Regards,
Ron

Offline Vixen

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Re: V8 cylinder firing order
« Reply #6 on: January 23, 2023, 08:56:00 PM »
Hi Mike. Thank you so very much for taking the time to respond so quickly and well to my question.

The 1-3-7-2-6-5-4-8 firing order strikes me as rather less intuitive than the others. Do you know what the reasoning behind that choice is?

Hi Ron,

You live in the land of the V8, they are still a rear breed in the UK. I am sure you will have a better feeling for the merits, or otherwise, of the different V8 engine types, hence your comment on the 1-3-7-2-6-5-4-8 firing order. I cannot add anything and the guys who made the decisions, all those years ago, are long gone.

Mike
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Offline RReid

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Re: V8 cylinder firing order
« Reply #7 on: January 23, 2023, 11:54:07 PM »
Fair enough! Thanks again, Mike. :cheers:
Regards,
Ron

Offline vtsteam

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Re: V8 cylinder firing order
« Reply #8 on: January 24, 2023, 01:35:58 AM »
Steve

Offline Vixen

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Re: V8 cylinder firing order
« Reply #9 on: January 24, 2023, 11:29:01 AM »
Thanks Steve'

As you know, I am not a native American V8 speaker. All I know about them comes off the net (and we know we can trust that?)


I followed Steve's Ford Muscle Car link and it revealed something interesting:

The Ford 1-3-7-2-6-5-4-8 and GM 1-8-7-2-6-5-4-3 firing orders are identical, they just use different cylinder numbering systems.

The alternative Ford 1-5-4-2-6-3-7-8 and the alternative GM 1-8-4-3-6-5-7-2 are also identical.

Whats more interesting is that the normal and alternative firing orders are also identical; they are simply mirror images of each other.  Have a look at this diagram to see what I mean.



That means there is really only ONE firing order for the V8, designed to reduce harmonic resonances in the crankshaft. It just gets dressed up differently between the manufacturers and engine models.

I already knew the cylinder firing order for the Mercedes Benz W165 was 1-3-7-2-6-5-4-8 and now I can confirm the cylinder numbering system which corresponds to it. I can now get on and make the camshafts to match.

I think this should have now have answered Ron Reid's original question     :Lol: :Lol:

Mike
« Last Edit: January 24, 2023, 01:55:56 PM by Vixen »
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Offline vtsteam

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Re: V8 cylinder firing order
« Reply #10 on: January 24, 2023, 01:51:25 PM »
I noticed that too when picking any pair of cylinders (not cylinder numbers) and seeing if that connection corresponded elsewhere. It did, though sometimes reversed R to L or L to R. Interesting also that they had names for the orders.

They also show (I believe) the direction of the distributor rotation, which can also vary. Thus a Babel of possibilities for running spark plug wires!
Steve

Offline RReid

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Re: V8 cylinder firing order
« Reply #11 on: January 24, 2023, 03:52:26 PM »
I had noted that the Ford "normal" and GM "normal" firing orders are equivalent, as are the Ford "alternative" and GM "alternative". But Mike's insight that the "normal" and "alternative" firing orders are simply mirror images really ties the whole thing together. So the underlying theory seems to be little more complex than that of a cylinder head bolt tightening sequence. The differences appear to arise mostly to satisfy notions of product differentiation or, over time, learned improvements in crank or bearing longevity.

I go to bed, and in the morning find that my homework has been done for me! Thanks guys!
Regards,
Ron

Offline Vixen

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Re: V8 cylinder firing order
« Reply #12 on: January 24, 2023, 05:18:30 PM »
So, here is my 1/3 scale Mercedes Benz W165 all roller bearing, built up, cross plane V8 crankshaft.

Note, the heavy counterweights, which are a characteristic feature of the cross plane configuration. In this engine, the counterweights are particularly big, as they have to offset the weight of the heavier roller bearing big end bearing.



In 1939, the Mercedes Benz W165, was very much a 'state of the art' racing engine. Most racing engines of the 1930's era used roller bearings for both the main and conrod bearings. They were more reliable than the available plain bearing but much more expensive to produce. The big end bearings tended to be quite large and bulky, therefore needed larger counterweights, which in turn needed a larger, bulkier, crankcase to contain the rotating parts.

Mike

« Last Edit: January 24, 2023, 07:40:44 PM by Vixen »
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Offline vtsteam

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Re: V8 cylinder firing order
« Reply #13 on: January 24, 2023, 09:38:13 PM »
Beautiful!! :ThumbsUp: :ThumbsUp: :ThumbsUp:

Oddly enough, though living in the land of 8 cyls, I've never owned a V-8 vehicle. Plenty of air cooled pancake 4s in the 60's and 70's, you can guess what they were, three straight 6s: a flathead in a '41 Plymouth pickup, one six in a 3/4 ton '57 S100 "Cornbinder" (can you figure that one out?), and another six with twin SU carbs and electric overdrive, bet you can guess that one!  One V-6 in an '85 vehicle named after the Jetson's dog, and my favorite all time vehicle (and a very plebeian one) a straight 4, with manual tranny in a '94 D21 "Hardbody". Gosh I miss her...!  :lolb:

Steve

Offline Vixen

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Re: V8 cylinder firing order
« Reply #14 on: January 24, 2023, 10:04:25 PM »
I will have a guess but probably wrong

VeeDub, International Harvester, Vitesse/ GT6 or maybe MG C

How did I do?   :embarassed:   0/3  1/3  2/3  3/3

Mike
« Last Edit: January 24, 2023, 10:50:17 PM by Vixen »
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Offline vtsteam

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Re: V8 cylinder firing order
« Reply #15 on: January 24, 2023, 11:48:59 PM »
2 out of 3 Mike! But the last was missing and I was sure you would get it. To get into overdrive the shifter had to be down hard on the tunnel, and there was an ordinary toggle switch in the dash, that you flipped.

This vehicle was VERY low to the ground. So much so that just going over the entry ramp at a gas station would knock my exhaust off sometimes! I got used to reattaching it fairly quickly. But the embarrassment factor was fairly high.

It had twin pipes which were, stock flexible tube off of the manifold. I often had a hard time convincing state inspection station mechancs that this was original, since flexible exhaust pipe was banned here. It had unusual lever arm shock absorbers that sat on pillars atop the front springs. Very hard to find replacements in the States. All in all an extremely impractical car in a Vermont winter, and yet...... it was mine! And I was very proud of it. After all, it cost $500 in real money.......well it was used of course!

I believe that if I still had it the price has gone up some.... :thinking:
Steve

Offline RReid

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Re: V8 cylinder firing order
« Reply #16 on: January 25, 2023, 12:43:52 AM »
Although I was the weird kid in high school who drove a clapped out Italian sports car rather than a clapped out V8 muscle car or truck, I have owned two V8 powered cars over the years. One a Jeep CJ-5 that a buddy and I swapped a Chevy 283 into, and a V8 Cornbinder Scout that I only put gas into. Also had one British sports car, a 1960 Tr-3. Didn't get seriously involved in engines themselves until after retirement, when I built a 1776cc VW motor using almost all new parts. Then found a '67 bug to put it into. A corner of that car shows up occasionally in some of my pics.
Regards,
Ron

Offline vtsteam

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Re: V8 cylinder firing order
« Reply #17 on: January 25, 2023, 03:36:00 AM »
Oh I remember building V-dub engines! Fond memories of the JC Whitney catalog. Jugs and distributors, cams. That was our bible. I at one point I in the early 70's made a VW dune buggy with an orange fiberglass body, purchased from a for sale ad in the local paper . Also a foolish car in VT winters!  But fun.

Okay Mike one more hint. You were close with the MGC. Except mine was a 1959 vintage vehicle.

Steve

Offline Vixen

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Re: V8 cylinder firing order
« Reply #18 on: January 25, 2023, 11:28:22 AM »
1959, I was still a schoolboy. :Lol:

The Big Healeys (Squeeeeeleys) were fitted with BMC C series engines, twin SU carbs, Laycock? overdrive and Armstrong lever arm shocks. The earliest Healeys had a weak back axle which were prone to stripping the splines off the half shafts. The interim 'fix' was a plate over the gear shift which prevented the selection of first gear.  :facepalm:

Was yours a late 100-6 or an early 3000? Either would be a handful on snow and ice  :censored:

Mike
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Offline vtsteam

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Re: V8 cylinder firing order
« Reply #19 on: January 25, 2023, 02:32:10 PM »
Mike, it was a 3000 Mark I with the horizontal wavy grille bars.

I was a schoolboy, too, when it was made. I first owned it ten years later. $500 was a lot of money at the time, to me, but they seem to have appreciated since then about 100 times, which puts it well above inflation. I of course sold it for less than I bought it for two years later, and bought another Vee-dub.
Steve

 

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